Conventionally, in air-conditioning equipment electric actuators have been used for performing operations for opening and closing valves that are installed within cold water or hot pipes, and operations for adjusting the openings of dampers in order to increase or decrease the flow rate of conditioned air that is supplied to an air-conditioned area through a duct.
In a normal electric actuator of this type, a motor is provided with in the electric actuator, to operate so as to cause the opening of the controlled element such as a valve or a damper to go to a setting opening in response to a control command from an air conditioner controller.
With this type of electric actuator, if there is an interruption to the power that is supplied, the degree of opening of the controlled element maintains the operating opening from immediately prior to the power outage, and appropriate opening control is no longer performed.
Given this, there have been proposals, that have been put into practice, for electric actuators of a type wherein, if there is an interruption to the power that is supplied to the electric actuator, it is forcibly driven to a specific opening (such as fully closed) and maintains that specific opening until the power supply is again restored to the normal state. In the below, this type of electric actuator will be termed “an electric actuator with an emergency shutdown function.”
At present, there are, specifically, two types of electric actuators with emergency shutdown functions that have been proposed, one type known as the spring return type, and the other type known as the secondary power supply driven type.
The spring return-type electric actuator is loaded with a return spring that applies a force on the driveshaft of the electric actuator so as to maintain a fully-closed state of the controlled element, where, when power is supplied, a driving motor is driven against the force applied by the return spring to adjust the opening of the controlled element, such as a valve or a damper, and if the power is interrupted the force applied by the return spring forcibly drives the controlled element, such as the valve or the damper, to the specific opening.
On the other hand, in the secondary power supply driven-type electric actuator, an electricity storing body structured from a storage battery or an electric double-layer capacitor or the like, is provided, where, when power is supplied, a motor is driven by the power supply to adjust the opening of the controlled element, such as a valve or a damper, and when the power is interrupted the electricity storing body is used as the operating power supply to drive the electric motor to drive the controlled element, such as the valve or the damper, forcibly to the specific opening.
However, when these two types of electric actuators with emergency shutdown functions are compared, in the spring return type the force applied by the return spring acts in resistance to the driving by the motor during normal operation, requiring the use of a motor with a large torque in order to overcome this resistance, and thus there is the shortcoming that this causes the electric actuator to be large, heavy, and costly.
In contrast, with the secondary power supply driven type, there is no shortcoming such as in the spring return type, and in recent years there have been improvements in the storage capacity of the storage batteries or electric double layer capacitors that serve as the electricity storing body, causing the secondary power supply driven-type electric actuator to be advantageous.
FIG. 12 illustrates a motor driving circuit for an electric shutdown valve set forth in, for example, Japanese Unexamined Patent Application Publication H11-101359 (the “JP '359”). In this figure, 1 is a commercial power supply, 2 is a power supply switch, 3 is a constant voltage circuit for converting an AC voltage into a specific DC voltage, 4 is a relay, 5 is a motor (DC motor), 6 is an opening-side limit switch, 7 is a closing-side limit switch, 8 and 9 are contact points (relay contact points) of the relay 4, 10 is an electricity storing body (electric double layer capacitor), 11 is a diode, and 12 is a resistance.
In this motor driving circuit, when the power supply switch 2 is turned ON, a DC voltage is outputted from the constant voltage circuit 3, magnetically exciting the relay 4, causing the relay contact points 8 and 9 to both switch to the terminals 8a and 9a. At this time, the motor 5 is in an intermediate opening state, where the opening-side limit switch 6 is at the terminal 6a side and the closing-side limit switch 7 is at the terminal 7a side. Moreover, let us assume that a full-open instruction has been received as an opening instruction.
Given this, the motor 5 rotates to drive the valve in the opening direction. Following this, when the opening-side limit switch 6 operates to switch to the terminal 6b side, that is, when the valve is fully open, the motor 5 stops. On the other hand, the electricity storing body 10 is charged through the resistance 12.
If, in this state, a power outage were to occur, then the DC voltage would cease to be outputted from the constant voltage circuit 3, the magnetic excitation of the relay 4 would disappear, and the relay contact points 8 and 9 would switch to the respective terminal 8b and 9b sides. At this time, the electric power stored in the electricity storing body 10 would flow through the diode 11 and the closing-side limit switch 7 to be supplied to the motor 5, to run the motor 5 in the opposite direction, to drive the valve in the closing direction. When the closing-side limit switch 7 operates to switch to the terminal 7b side, that is, when the valve is fully closed, the motor 5 stops.
However, with the motor driving circuit illustrated in FIG. 12, during maintenance there are cases wherein one may wish to maintain the valve opening at an arbitrary position other than being fully closed with the power supply switch 2 OFF, and in such cases it is necessary to discharge the power that is stored in the electricity storing body 10.
That is, when, during maintenance, the power supply switch 2 is turned OFF, the motor 5 is forcibly driven by the electric power that is stored in the electricity storing body 10, because a situation that is identical to that of a power outage has occurred, so the valve will fully close. When, in such a state, one attempts to move this fully-closed valve in the opening direction, the closing-side limit switch 7 switches to the terminal 7a side, and the supply of electric power from the electricity storing body 10 to the motor 5 is restarted, so the motor 5 attempts to return the valve to the fully-closed state.
Consequently, when, at the time of maintenance, one wishes to turn the power supply switch 2 OFF and maintain the valve opening at an arbitrary position other than fully closed, it is necessary to discharge the electric power that is stored in the electricity storing body 10 until the motor no longer attempts to return the valve to the fully-closed state. Because of this, not only does this produce waiting time in the operation, waiting for the discharge to be complete, but also wastes the electric power that is discharged.
Note that Japanese Patent 4774207 (the “JP '207”) shows a shutdown valve equipped with a switch and power supply monitoring means between a rechargeable power supply (electricity storing body) and actuator (motor), where, when the power supply monitoring means detect a power outage, the switch is turned ON to connect the rechargeable power supply to the actuator, where, when the actuator is operated by the connected rechargeable power supply and becomes fully closed, the switch turns OFF, to terminate the connection between the rechargeable power supply and the actuator, where the valve can be opened using an opening/closing handle.
FIG. 13 illustrates a motor driving circuit contemplating the application of the technology shown in the JP '207. In this motor driving circuit, a switch 13 that is configured corresponding to the switch described in the JP '207 is provided and a power supply monitoring portion 14, structured corresponding to the power supply monitoring means, is provided. The power supply monitoring portion 14 detects a power outage to turn the switch 13 ON.
In the configuration illustrated in this FIG. 13, when, at the time of maintenance, the power supply switch 2 is turned OFF, not only do the relay contact points 8 and 9 switch to the terminal 8b and 9b sides, but the switch 13 is turned ON by the power supply monitoring portion 14, and the electric power that is stored in the electricity storing body 10 is supplied to the motor 5 through the diode 11, the closing-side limit switch 7 and the switch 13. Doing so causes the motor 5 to rotate in the opposite direction, so the valve is driven in the closing direction. When the closing-side limit switch 7 operates to switch to the terminal 7b side, that is, when the valve is fully closed, the motor 5 stops. Moreover, when the valve is fully closed, the switch 13 is turned OFF.
Once the switch 13 has been turned OFF, then the OFF state is maintained regardless of the state of opening/closing of the valve. Because of this, when the handle is operated manually to drive the valve open, the electric power that is stored in the electricity storing body 10 is not supplied to the motor 5, notwithstanding the closing-side limit switch 7 operating to switch to the terminal 7a side. Because of this, it is possible to manually drive the valve open, even without discharging the electric power that is stored in the electricity storing body 10.
However, while, with this configuration, it is necessary to turn the switch 13 ON in order to restore the normal operating state after maintenance has been completed, when the operation for returning the switch 13 to ON (the operation for restoring the normal operating state) is performed manually, there is the possibility that there will be forgotten the restoration operation. Moreover, while one may consider providing timing means to turn the switch 13 ON after a specific amount of time has elapsed after the valve is closed, based on the time of the timing means, there is a problem that this constrains the time over which the valve can be opened and closed manually.
The present invention was created to solve such problems, and an aspect thereof is to provide an electric actuator wherein maintenance can be performed without a completely discharging the electric power that is stored in the electricity storing body, without forgetfulness of the operation for restoring the normal operating state, and without time constraints.
Moreover, it is to provide an electric actuator wherein it is possible to switch to a maintenance mode without shutting off the external power supply, that is, while still in a powered state.